<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>变量</title>
</head>
<body>
    <script>
        console.log( isNaN(NaN) );  //返回true
        console.log( isNaN("123") );  //返回false(可以被转换成数值123)
        console.log( isNaN("hello") );  //返回true(不能被转换成数值)
        console.log( isNaN(true) );  //返回false(可以被转换成数值1)
    </script>
</body>
</html>